Fermi telescope spots 'superflares' in the Crab Nebula (w/ video)

May 12, 2011

A Hubble visible light image of the Crab Nebula inset against a full-sky gamma ray map showing the location of the nebula (croshairs). Credit: NASA

(PhysOrg.com) -- The famous Crab Nebula supernova remnant has erupted in an enormous flare five times more powerful than any flare previously seen from the object. On April 12, NASA's Fermi Gamma-ray Space Telescope first detected the outburst, which lasted six days.

The nebula is the wreckage of an exploded star that emitted light which reached Earth in the year 1054. It is located 6,500 light-years away in the constellation Taurus. At the heart of an expanding gas cloud lies what is left of the original star's core, a superdense neutron star that spins 30 times a second. With each rotation, the star swings intense beams of radiation toward Earth, creating the pulsed emission characteristic of spinning neutron stars (also known as pulsars).

Apart from these pulses, astrophysicists believed the Crab Nebula was a virtually constant source of high-energy radiation. But in January, scientists associated with several orbiting observatories, including NASA's Fermi, Swift and Rossi X-ray Timing Explorer, reported long-term brightness changes at X-ray energies.

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There are strange goings-on in the Crab Nebula. On April 12, 2011, NASA's Fermi Gamma-ray Space Telescope detected the most powerful in a series of gamma-ray flares occurring somewhere within the supernova remnant.

"The Crab Nebula hosts high-energy variability that we're only now fully appreciating," said Rolf Buehler, a member of the Fermi Large Area Telescope (LAT) team at the Kavli Institute for Particle Astrophysics and Cosmology, a facility jointly located at the Department of Energy's SLAC National Accelerator Laboratory and Stanford University.

Since 2009, Fermi and the Italian Space Agency's AGILE satellite have detected several short-lived gamma-ray flares at energies greater than 100 million electron volts (eV) -- hundreds of times higher than the nebula's observed X-ray variations. For comparison, visible light has energies between 2 and 3 eV.

On April 12, Fermi's LAT, and later AGILE, detected a flare that grew about 30 times more energetic than the nebula's normal gamma-ray output and about five times more powerful than previous outbursts. On April 16, an even brighter flare erupted, but within a couple of days, the unusual activity completely faded out.

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Scientists hoped that NASA's Chandra X-ray Observatory would locate X-ray sources correlated to the gamma-ray flares seen by Fermi and Italy's AGILE satellites. Two observations were made during the April 2011 superflare, but there's no clear evidence of them in the Chandra images. Credit: NASA/CXC/MSFC/M.Weisskopf and A. Tennant.

"These superflares are the most intense outbursts we've seen to date, and they are all extremely puzzling events," said Alice Harding at NASA's Goddard Space Flight Center in Greenbelt, Md. "We think they are caused by sudden rearrangements of the magnetic field not far from the neutron star, but exactly where that's happening remains a mystery."

The Crab's high-energy emissions are thought to be the result of physical processes that tap into the neutron star's rapid spin. Theorists generally agree the flares must arise within about one-third of a light-year from the neutron star, but efforts to locate them more precisely have proven unsuccessful so far.

Since September 2010, NASA's Chandra X-ray Observatory routinely has monitored the nebula in an effort to identify X-ray emission associated with the outbursts. When Fermi scientists alerted astronomers to the onset of a new flare, Martin Weisskopf and Allyn Tennant at NASA's Marshall Space Flight Center in Huntsville, Ala., triggered a set of pre-planned observations using Chandra.

"Thanks to the Fermi alert, we were fortunate that our planned observations actually occurred when the flares were brightest in gamma rays," Weisskopf said. "Despite Chandra's excellent resolution, we detected no obvious changes in the X-ray structures in the nebula and surrounding the pulsar that could be clearly associated with the flare."

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Video of Crab flare sequence. Credit: NASA/DOE/Fermi LAT/R. Buehler

Scientists think the flares occur as the intense magnetic field near the pulsar undergoes sudden restructuring. Such changes can accelerate particles like electrons to velocities near the speed of light. As these high-speed electrons interact with the magnetic field, they emit gamma rays.

To account for the observed emission, scientists say the electrons must have energies 100 times greater than can be achieved in any particle accelerator on Earth. This makes them the highest-energy electrons known to be associated with any galactic source. Based on the rise and fall of gamma rays during the April outbursts, scientists estimate that the size of the emitting region must be comparable in size to the solar system.

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A potential beacon? (i know this is silly) but what if a race had the technology to use these pulsars as a form of a beacon to attract attention? and what better way to reach even races who have not yet found a way to travel among the stars... speculation for sure, but what if?

The US National Academy of Sciences, the UK's Royal Society, the UN's IPCC, world leaders (Al Gore & Associates), and government research agencies, leading research journals (Nature, Science, Proceedings of the US National Academy and the UK's Royal Society) and the news media (BBC, PBS, CBS, The New York Times, etc) need to:

LaViolette has proposed that this is simply a Milky Way galactic core cosmic ray electron volley superwave propagating through and illuminating the existing nebula. It is a transient event, lasting perhaps thousands of years.

Note: "Despite Chandra's excellent resolution, we detected no obvious changes in the X-ray structures in the nebula and surrounding the pulsar that could be clearly associated with the flare."

"LaViolette has proposed that this is simply a Milky Way galactic core cosmic ray electron volley superwave propagating through and illuminating the existing nebula. It is a transient event, lasting perhaps thousands of years."

If LaViolette has proposed that the pulsar and illuminated nebula in the Crab Nebula is perhaps "thousands of years old", where can I find his peer reviewed paper published in a relevant (astrophysical) publication? I'd love to see his quantative method for age determination.

In the meantime, Rudie et al have published a 2008 paper that carefully looks at the observed motions of 35 locations of specific features of the Crab over a 20 year period using images from the 4m KPNO and 8.2m Subaru scopes: http://arxiv.org/...93v1.pdf

Meticulous observations of the movement of these filaments indicate the supernova occurred in 1055 +-24 C.E., VERY close to the date of the "guest star" observed by Chinese and Arab astronomers in 1054 C.E.

LaViolette does not challenge the age of the event, only the potential duration of the passing superwave, which (I understand) may range range from hundreds to perhaps a thousand years or so. Just happens to be passing through this nebula at the current time (from our perspective). Thus we see the nebula illuminated.

Anyway, if the origin of the cosmic rays were a galactic core expulsion, might this explain the cosmic ray energies involved. Perhaps we are witnessing a moment of peak intensity of the wave passing a particularly strong or aligned magnetic structure within the nebula (my speculation only).

Mr. Manuel, neutron stars have been assumed to be active with starquakes, pulsars, magnetars, etc, but we did learn from your neutron repulsion theory that neutron stars are impossible. This neutron star must be a figment of someone's imagination.

@LKD, Masked MarauderIt does seem like a more productive means of communication than other interstellar methods. I'm with LKD tho, that a race able to do that would have found a way to communicate FTL, if there is a way.

Correct me, but I thought "flares" came from active Suns? If a neutron star is capable of being active, then it would by all means emit and shed unwanted "waste" in the form of flares. Our Sun emits solar flares. What would be so strange for any active Sun to emit "solar flares" from its surface? Has the neutron star been located?

"LaViolette does not challenge the age of the event, only the potential duration of the passing superwave, which(I understand) may range range from hundreds to perhaps a thousand years or so. Just happens to be passing through this nebula at the current time(from our perspective). Thus we see the nebula illuminated."

Do you have a published ref for this notion(in a relevant refereed pub)?

How would the nucleus of the MWG produce the *observed* highly energetic synchrotron radiation illuminating a nebula 13ly in diameter from a distance of 35kly AND no other nebulae at the same distance and location of the Crab?

Wouldn't a passing "superwave" appear as a linear feature across the Crab Neb? How would it explain the expanding ring of X-ray emission from the pulsar, recently observed by Chandra?: http://chandra.ha...11/crab/

The Crab Nebula is *observed* to be powered by its pulsar. You have presented NO observations that say otherwise, only ill-informed suppositions.

Please direct me to a published SED of the total EM output of the Crab Nebula derived from quantitative neutron repulsion models of the Crab pulsar. I would like to compare this curve in some detail with the observed SED.

This should be a trivial request in light of the many studies of the Crab pulsar over many years.